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Lackner, a
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energy expert at Columbia University, has designed an
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tree that soaks up carbon dioxide from the air using "leaves" 1,000 times more efficient than true leaves. He explains: The leaves are
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in a resin that contains sodium carbonate, which pulls carbon dioxide out of the air and stores it as a bicarbonate on the leaves. To remove the carbon dioxide, the leaves are
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in water
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and can dry naturally in the wind, soaking up more carbon dioxide.
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that our total
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could be removed with 100 million trees. The removed carbon dioxide can be
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and stored; however, there isn"t enough space to store it. But
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are coming up with
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, for example, peridotite, which is a great
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of carbon dioxide. Another
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could be the basalt rock
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, which contain
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gas bubbles.
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carbon dioxide into these bubbles causes it to form
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limestone. However, Lackner thinks the gas is very useful and it can be used to make
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fuels for transport
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. We have the technology to suck carbon dioxide out of the air, and keep it out, but whether it is economically
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is a different question. We have to decide whether the cost of the technology is socially and economically
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the price.
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implication[听力原文]Last week we discussed some key terms widely used in dealing with environmental protection. I m sure they are still fresh in your mind. Right So in today s environmental science class, I want to discuss a few other terms here, actually some ideas about how we manage our resources. Let s talk about what that means. If we take resources like water, now maybe we should get a little bit more specific here, back from more general cases and talk about underground water in particular. So hydro geologists have tried to figure out how much water can we take out from underground sources. That has been an important question. Let me ask you guys, how much water, based on what you know so far, could you take out of, say, an aquifer under the city. As much as what gets rechargedOK. So we wouldn t like to take out more than naturally comes into it. The implication is that, well, if you only take as much out as comes in, you re not going to deplete the amount of water that stores in there. Right Wrong. But that s the principle. That s the idea behind how we manage our water supplies. It s called safe yield. Basically what this message says is that you can pump as much water out of the system as naturally recharges, as naturally flows back in. So this principle of safe yield is based on balancing what we take out with what gets recharged. But what it does is it ignores how much water naturally comes out of the system. In a natural system a certain amount of recharge comes in and a certain amount of water naturally flows out through springs, streams and lakes, and over the long term the amount that s stored in the aquifer doesn t really change much. It s balanced. Now humans come in and start taking water out of the system. How have we changed the equation It s not balanced any moreRight. We take water out but water also naturally flows out. And the recharge rate doesn t change. So the result is we ve reduced the amount of water that stores in the underground system. If you keep doing that long enough, if you pump as much water out as naturally comes in, gradually the underground water level will drop. And when that happens, they can t fix service water. How Well, in underground systems there are natural discharge points, places where the water flows out from the underground systems, out of lakes and streams. Well, a drop of water level can mean those discharge points will eventually dry up, and that means water s not getting to lakes and streams that depend on it. So we end up reducing the surface water supply, too. You know, in the state of Arizona, we re managing some major water supplies with the principle of safe yield and under this method they will eventually dry up the natural discharge points of those aquifer systems. Now, why is this issue Well, aren t some of you going to want to live in the state for a while Won t your kids grow up here, and your kids kids You may be concerned with Does Arizona have water supply which is sustainable Key word here. What does sustainable mean The general definition of sustainable is whether it is enough to meet the needs of the present without compromising the ability of the future to have the availability to have the same resources.Now, I hope you see these two ideas are incompatible: sustainability and safe yield. Because what sustainability means is that it s sustainable for all systems that depend on the water, for the people who use it, and for supplying water to the dependent, like some streams. So I m going to repeat this. So, if we are using a safe yield method, we re only balancing what we take out with what gets recharged, but don t forget, water also flows out naturally. Then the amount stored underground gradually gets reduced, and that is going to lead to another problem: the lakes and streams are going to dry up. OK
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